Klothys's Design — ruling 1

Mana symbols in the text boxes of permanents you control don’t count toward your devotion to any color.

Klothys's Design — ruling 2

Klothys’s Design affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +X/+X.

Klothys's Design — ruling 3

Colorless and generic mana symbols ({C}, {0}, {1}, {2}, {X}, and so on) in mana costs of permanents you control don’t count toward your devotion to any color.

Klothys's Design — ruling 4

The value of X is determined only as Klothys’s Design resolves. Once that happens, the value of X won’t change later in the turn even if your devotion to green changes.

Klothys's Design — ruling 5

Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).

Klothys's Design — ruling 6

If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it’s still on the battlefield at that time.

Klothys's Design — ruling 7

If you put an Aura on an opponent’s permanent, you still control the Aura, and mana symbols in its mana cost count towards your devotion.

Klothys's Design : règles, fonctionnement et interactions (MTG)

Klothys's Design is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Creatures you control get +X/+X until end of turn, where X is your devotion to green. (Each in the mana costs of permanents you control counts toward your devotion to green.)

How it works : Klothys's Design

Original English text — Wizards of the Coast / Scryfall

#1January 24, 2020· Wizards of the Coast
Mana symbols in the text boxes of permanents you control don’t count toward your devotion to any color.
No other card is named in this ruling.
#2January 24, 2020· Wizards of the Coast
Klothys’s Design affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +X/+X.
No other card is named in this ruling.
#3January 24, 2020· Wizards of the Coast
Colorless and generic mana symbols (, , , , , and so on) in mana costs of permanents you control don’t count toward your devotion to any color.
No other card is named in this ruling.
#4January 24, 2020· Wizards of the Coast
The value of X is determined only as Klothys’s Design resolves. Once that happens, the value of X won’t change later in the turn even if your devotion to green changes.
No other card is named in this ruling.
#5January 24, 2020· Wizards of the Coast
Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
No other card is named in this ruling.
#6January 24, 2020· Wizards of the Coast
If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it’s still on the battlefield at that time.
No other card is named in this ruling.
#7January 24, 2020· Wizards of the Coast
If you put an Aura on an opponent’s permanent, you still control the Aura, and mana symbols in its mana cost count towards your devotion.
No other card is named in this ruling.